PROJECT SUMMARY Lung transplantation is increasingly used to treat patients with end-stage lung diseases. Complications frequently occur with chronic allograft rejection causing most of late morbidity and mortality in lung transplant recipients. Pathological manifestations of chronic rejection mostly affect small airways or bronchioles in the lung, often progressing undetected until the patient presents with an irreversible decline in pulmonary function. There is an unmet need for safe and accurate methods to detect and classify earlier, sub-clinical lesions associated with subsequent development of chronic rejection in asymptomatic patients, to maximize preservation of lung function in these patients. The goal of this project is to build and evaluate a clinical instrument that is capable of 3D imaging of bronchioles and surrounding parenchyma to address this unmet need. With this instrument, clinicians will be able to identify, minimally-invasively, dimensional and structural changes of small airways and alveoli, and to detect vascular and fibrotic abnormalities in the airways. The instrument will rapidly scan many branches of sub-segmental bronchioles for reliable and accurate classification of early pathologies leading to chronic rejection to indicate earlier and more targeted therapeutic interventions. Our proposed instrument is based on a miniaturized flexible endobronchial imaging probe that combines multi-modality optical coherence tomography with autofluorescence imaging. This high resolution and high-capability imaging, recently developed by our academic collaborators, has been shown to accurately and rapidly visualize fine anatomical structures of small airways and alveoli, also identifying pulmonary vasculature and lung fibrosis. Towards the objective of developing and evaluating such a clinical instrument, we will first improve the existing prototypes (Aim 1) to enhance image features associated with relevant pathologies in the lung graft. We will validate the improved performance using test fixtures and live animals. Aim 2 is to evaluate the readiness of the improved instrument for human trials by conducting appropriate safety and performance tests for the device. In Aim 3, we will evaluate the multi-modality endobronchial imaging probe in clinical trials aimed at collecting a library of images of lung transplant patients and identifying diagnostic criteria in the image data for detection of abnormalities associated with chronic rejection of lung allograft. We will image asymptomatic patients during their regular post-transplant exams and patients with established lung transplant dysfunction. We will correlate relevant image features with lung function, histology and bronchoalveolar lavage findings, and other clinical parameters and clinical history in these two groups of patients.